Rake device for a three wheel motorcycle

ABSTRACT

A method of modifying the rake angle on a motorcycle having a double wishbone front suspension. The motorcycle has a tubular steering housing connected to a non-telescoping fork assembly by a straight body steering stem. The method includes the step of replacing the straight body steering stem with a canted body steering stem. The canted body steering stem includes (i) a primary section having a steering axis corresponding to a steering axis of the motorcycle; and (ii) a secondary section having a cant axis which varies from the steering axis by between 1° and 16°.

CROSS-REFERENCE TO RELATED APPLICATION

This application claims the benefit under 35 USC § 119 to U.S.Provisional Application Ser. No. 62/717,262 filed Aug. 10, 2018 andwhich is incorporated by reference herein in its entirety.

BACKGROUND OF INVENTION

The present invention relates to steering mechanisms for motorcycles andmore specifically, modifying the rake angle of the steering mechanism.

Traditional motorcycle steering/front suspension designs often havetriple trees and telescoping forks with spring and shock absorbingfunctions being internal to the forks. The steering system includes asteering axis and a steering axis angle. The steering axis is the axisabout which the steering mechanism (fork, handlebars, front wheel, etc.)pivots, and usually matches the angle of the head tube. The steeringaxis angle is the angle that the steering axis makes with the horizontalor vertical, depending on convention. In motorcycles, the steering axisangle is typically called the “rake angle” (or just “rake”) and ismeasured from the vertical, e.g., a 0° rake would be vertical. The“trail” is the horizontal distance from where the front wheel touchesthe ground to where the steering axis intersects the ground. With atraditional triple tree front suspension, the rake is normally modifiedby changing the angle of the down tubes relative to the steering stem.This moves the tire contact patch closer to where the steering axisintersects the ground and reduces the trail, thereby reducing thesteering effort.

However, certain motorcycle designs such as the 2018 Honda® Goldwing®have a double wishbone front suspension similar to a car. In thisdesign, there are no telescoping forks to house the spring/shockassembly. Instead, the forks are rigid and there is a separate coil overshock that bolts between a lower control arm and the motorcycle frame.One rake modification (“rake kit”) for this type of suspension is tochange the length of the upper and lower control arms, but this movesthe steering axis along with the front wheel (similar to a “chopper”style motorcycle) and it does not reduce trail with particulareffectiveness. It also changes ride quality by changing the leverage thesuspension has on the shock. A better method for modifying the rake ondouble wishbone type steering/suspension systems would be a desirableadvancement in the industry.

SUMMARY OF SELECTED EMBODIMENTS OF INVENTION

One embodiment of the invention is a motorcycle steering systemconfigured for connection to a motorcycle frame. The steering systemincludes a tubular steering housing attachable to the motorcycle frameby at least one control arm. A spring assembly is positioned either (i)between the control arm and the motorcycle frame, or (ii) between thesteering housing and the motorcycle frame. A non-telescoping forkassembly is positioned below the steering housing, while a steering stemis positioned at least partially within the steering housing. Thesteering stem includes a secondary section attaching to the forkassembly and a primary section having a steering axis. The secondarysection has a cant axis varying from the steering axis by between atleast 1° and about 16°.

Another embodiment of the invention is a method of modifying the rakeangle on a motorcycle having a double wishbone front suspension. Themotorcycle will have a tubular steering housing connected to anon-telescoping fork assembly by a straight body steering stem. Themethod will include the step of replacing the straight body steeringstem with a canted body steering stem. The canted body steering stemwill include (i) a primary section having a steering axis correspondingto a steering axis of the motorcycle; and (ii) a secondary sectionhaving a cant axis which varies from the steering axis by between 1° and16°.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a side view of the general frame of a motorcycle having adouble wishbone front suspension.

FIG. 2 is a perspective view of the front motorcycle frame and thedouble wishbone suspension.

FIG. 3A is a sectional view of the front motorcycle frame and the doublewishbone suspension.

FIG. 3B is a detailed portion of the FIG. 3A view.

FIG. 4A is a cross-section of a prior art steering stem.

FIG. 4B is a cross-section of one embodiment of a steering stem of thepresent invention.

FIG. 5 is a side view illustrating a change in trail.

FIG. 6 is a sectional view of a second embodiment of the steering stemof the present invention.

DETAILED DESCRIPTION OF SELECTED EMBODIMENTS OF INVENTION

FIG. 1 illustrates a general frame of a motorcycle having a doublewishbone front suspension, with rear wheel 67, front wheel 66, and thefront portion of the motorcycle frame 65. Fork assembly 40 engagessteering housing 5 which is connected to frame 65 by front suspensionassembly 75. The steering axis 13 extends through steering housing 5 tointersect the ground. The trail 50 can be seen as the horizontaldistance from where the front wheel touches the ground to where thesteering axis intersects the ground. Although FIG. 1 suggests a twowheel motorcycle, the following disclosure applies equally to threewheel motorcycles with a rear axle driving two rear wheels (oftenreferred to as a “trike”); see for example the three wheel motorcycle inU.S. Pat. No. 6,964,314, which is incorporated by reference herein inits entirety. The same front portion of the frame is used in both twowheel and three wheel motorcycles. Thus, the term “motorcycle” as usedherein is intended to cover both two wheel and three wheel motorcycles.

The overall steering system 1 of the motorcycle is best seen in FIGS. 2and 3A. The handle bars 70 will pivotally engage handle bar column 71,which is part of front frame 65. The rotating motion of handling bars 70is transmitted through steering tie rods 73, to the steering yoke 74,and ultimately to steering stem 10 (which is more clearly seen in FIG.3A and is largely internal to steering housing 5). Nevertheless, anupper end of steering stem 10 extends above steering housing 5 to engagesteering yoke 74 while a lower end extends below steering housing 5 toengage fork assembly 40. In other words, steering stem 10 extends atleast partially from steering housing 5 to engage fork assembly 10 andsteering yoke 74. With this linkage, the steering stem 10 transferssteering torque to fork assembly 40, which of course turns the frontwheel 66 of the motorcycle. This embodiment of fork assembly 40 is arigid, non-telescoping type of fork assembly.

Additionally, the suspension assembly 75 provides the shock absorbingfunction between wheel displacement transmitted through steering housing5 and front motorcycle frame 65. Suspension assembly 75 includes theupper control arm 80 and the lower control arm 85 which forms a rotativeconnection between lower control arm 85 and frame 65. The spring/shockassembly 76 is pivotally connected at one end to stem housing 5 and atits opposite end to frame 65. In this manner, spring/shock assembly 76acts to dampen relative rotation between stem housing 5 and frame 65 onthe control arms 80 and 85. In the illustrated embodiment, spring/shockassembly 76 is a conventional spring over piston type of shock absorber.However, spring/shock assembly could also be only a spring, only apiston, or another type of shock absorber that provides a dampening orspring effect. The term “spring assembly” will be used to describe anyof the foregoing or any future developed shock absorbing device thatprovides a spring-like dampening effect.

As best seen in FIG. 3A, the steering stem 10 extends through steeringhousing 5 and acts to transfer torque from steering yoke 74 to forkassembly 40. This embodiment of steering stem 10 is shown in isolationin FIG. 4B. For comparison, a prior art steering stem 100 is shown inFIG. 4A. In the FIG. 4B embodiment, steering stem 10 is formed of anelongated tubular stem body 11, although other embodiments of stem body11 could be a solid section of material, typically either aluminum orsteel. Stem body 11 has a primary section 12 which is typically at least75% of the length of the entire stem body. The primary section 12 ofstem body 11 is concentric around the axis 13 which also forms thesteering axis of the motorcycle. In the FIG. 3A embodiment, the primarysection 12 of the steering stem 10 is also oriented as the “uppersection” of the steering stem. Thus, the pin slot 25 is engaged by asteering yoke pin 78 and the threaded section 26 is engaged by lock nut7, as both seen in FIG. 3A. Stem body 11 also includes a secondarysection 15 (a “lower section” in the FIG. 3A orientation) which isconcentric around a secondary axis 16. Because secondary axis 16 is“canted” at an angle relative to steering axis 13, secondary axis 16will also be referred to as “cant axis” 16. In many embodiments, theangle “alpha” between steering axis 13 and cant axis 16 is between 1°and about 16° (or any sub-range in between). A more preferred range ofalpha is between about 4° and about 10°, with one specific example ofalpha being about 7°. The angle alpha may also sometimes be referred toas the “cant angle.” Likewise, the steering stem 10 may sometimes bereferred to as a “canted body” steering stem. Secondary section 15 ofstem body 11 also includes a collar section 19 with bolt apertures 20and the pin aperture 24. Overall, steering stem 10 will be, as measuredalong the length of the two axes, between about 5% and about 25% (or anysub-range in between) longer than the prior art “straight” steering stem100 such as seen in FIG. 4A for a given model of motorcycle and whichmay be presumed to be the original equipment steering stem for themotorcycle as sold by the manufacturer. In many embodiments, steeringstem will range in length between about 6″ and about 16″ inches (or anysub-range in between), with more preferred embodiments being 10″ to 14″.In many embodiments, the canted body steering stem will have“exclusively” two sections with two different (nonparallel) axes, i.e.,the canted body will not have a third section with a third axis.

Returning to FIG. 3A, it is seen how the secondary section 15 of stembody 11 will engage (generally with a friction fit) the stem aperture 41formed in fork assembly 40 until collar 19 abuts the top of stemaperture 41. A pin (not shown) will extend through the wall of stemaperture 41 and engage the pin aperture in stem secondary section 15 toensure fork assembly 40 and steering stem 10 are fixed against relativelateral (along axis 16) and rotative movement. A fork stop extension 22will be bolted to collar 19 with bolts threaded into bolt apertures 20.Fork stop extension 22 serves the same function as prior art fork stops,i.e., limiting how far the fork assembly can rotate right or left.However, the prior art fork stops may be prevented from engaging theirintended stop surfaces due to the additional length of steering stem 10as compared with the prior art steering stem 100. FIG. 3A furtherillustrates the upper bearing assembly 6 and the lower bearing assembly8 positioned between steering housing 5 and steering stem 10. Thesebearing assemblies allow free rotation of steering stem 10 inside ofsteering housing, thus transferring torque from the handle bars 70 tothe fork assembly 40 in the lowest friction manner practical. In theillustrated embodiment, the bearings engage the primary section of thesteering stem, i.e., the steering stem transitions to the cant axisbelow the lower bearing surface.

As described above, the “trail” is the horizontal distance from wherethe front wheel touches the ground to where the steering axis intersectsthe ground. For example, if it is assumed that FIG. 1 illustrates amotorcycle with the straight steering stem 100 of FIG. 4A, FIG. 1 showsthe steering axis 13 intersecting the ground and the point where thefront wheel touches the ground (directly below the front wheel axial),producing an indicated trail 50 of 4 5/16 inches. On the other hand, ifFIG. 5 illustrates a motorcycle with the canted steering stem 10 seen inFIG. 4B, then the front wheel axial is moved forward (as is the pointwhere the front wheel rests on the ground). Because the point of wheelcontact with the ground is now closer to the point where the steeringaxis 13 intersections the ground, the trail 50 has been reduced to asmaller distance of 1⅞ inches. Naturally these specific trail distancesare merely examples and trail length or distance may vary considerablyamong different motorcycle manufacturers and models. In manyembodiments, the trail distance will be between 1″ and about 3.5″. Itwill be apparent how varying the cant angle and overall length of thesteering stem 10 provides a simple, reliable, and economical manner ofadjusting the trail length.

FIG. 6 shows an alternate embodiment of the steering stem illustrated assteering stem 10A. This embodiment of the steering stem is substantiallyidentical to the FIG. 4B embodiment, except the secondary section 15does not have a canted axis relative to the steering axis. In FIG. 6,the secondary section 15 of steering stem 10A is “offset” from andoriented parallel to primary section 12. In other words, the secondaryaxis 16 is offset from and parallel to steering axis 13. In theillustrated embodiment, secondary axis 16 is offset from steering axis13 by a distance “d” of between about 0.25″ and about 7.0″ (or anysub-range in between), and more preferably, between about 0.5″ and about5.0″. Although FIGS. 4B and 6 illustrate two embodiments of a modifiedsteering stem having two axes, it is understand that the presentinvention could cover other steering stems having two sections, with onesection being concentric around a steering axis and the other sectionbeing concentric around a second, different axis.

A further embodiment of the present invention includes a method ofmodifying the rake angle on a motorcycle having a double wishbone frontsuspension. The motorcycle will have a tubular steering housingconnected to a non-telescoping fork assembly by a straight body steeringstem. The method will include the step of replacing the straight bodysteering stem with a canted body steering stem. The canted body steeringstem will include (i) a primary section having a steering axiscorresponding to a steering axis of the motorcycle; and (ii) a secondarysection having a cant axis which varies from the steering axis bybetween 1° and 16°, and more preferably 3° and 10°. Similarly, thecanted body steering stem will typically be about 5% and about 25%longer than the prior art straight body steering stem.

The term “about” will typically mean a numerical value which isapproximate and whose small variation would not significantly affect thepractice of the disclosed embodiments. Where a numerical limitation isused, unless indicated otherwise by the context, “about” means thenumerical value can vary by +/−5%, +/−10%, or in certain embodiments+/−15%, or even possibly as much as +/−20%. Similarly, “substantially”will typically mean at least 85% to 99% of the characteristic modifiedby the term. For example, “substantially all” will mean at least 85%, atleast 90%, or at least 95%, etc.

The invention claimed is:
 1. A method of modifying the rake angle on amotorcycle having a double wishbone front suspension, including atubular steering housing connected to a non-telescoping fork assembly bya straight body steering stem, the method comprising the step of: (a)replacing the straight body steering stem with a twin axis steeringstem, wherein the twin axis steering stem includes: (i) a primarysection having a steering axis corresponding to a steering axis of themotorcycle; and (ii) a secondary section having a secondary axis,wherein the secondary axis is offset from and parallel with the steeringaxis.
 2. The method according to claim 1, wherein the secondary axis isparallel to and offset from the steering axis by between 0.25″ and 7.0″.3. The method according to claim 2, wherein the secondary axis isparallel to and offset from the steering axis by between 0.5″ and 5.0″.4. The method according to claim 1, wherein at least two-thirds of alength of the steering stem is concentric around the steering axis. 5.The method according to claim 1, wherein the secondary section is lessthan 25% of an overall length of the primary section.
 6. The methodaccording to claim 1, wherein the steering stem reduces a trail of themotorcycle to less than 3 inches.
 7. The method according to claim 1,wherein the motorcycle is a three-wheel motorcycle having two rearwheels.
 8. The method according to claim 1, wherein a collar sectionextends from the stem body at a transition point of the primary sectionto the secondary section.
 9. The method according to claim 1, furthercomprising an upper and lower control arm connecting the steeringhousing to the motorcycle frame.
 10. The method according to claim 1,wherein a steering yoke connects to an uppermost portion of the steeringstem.
 11. The method according to claim 1, wherein at least part of thesecondary section of the steering stem inserts into the fork assembly.